Among other things, this application describes methods, apparatus and techniques for re-introducing iron-rich mill scale back into the basic iron and/or steel process stream whereby valuable economic and environmental benefits may be obtained. Mill scales (essentially iron oxides) are a generally little-exploited but highly available byproduct of standard production procedures. In this application, there is provided more details on a system and method for introducing mill scale (or other materials, including other waste materials) into a conventional Blast Furnace (BF) or other metallurgical process, such as making or refining a metal or making and compounding alloys). The described systems and methods are also suited to the utilization of wastes containing combustible matter as sources of metallurgical process heat and useful chemical elements.
The processing of iron and steel generates huge amounts of waste material consisting of small particles of iron oxide and other so-called “fines” and scrap—the former being typified by oxide-rich sand-like grains and brittle pieces of both larger and smaller size. Many techniques have been applied to the difficult challenge of economically recycling such materials. Generally these recovery and recycling methods require crushing the waste to relatively small size, mixing the ferrous material with various chemicals that may include fluxes and carbon-containing reducing agents such as ground coke, adding water and binding compounds such as cement, pelletizing the mixture, aging and drying the so-called green pellets, and, in the particular process known as hot briquetting, the exposing the pellets to high temperatures to convert the oxides. A major reason for such procedures is the high velocity gas flows that the material encounters during down-stream recycling operations (such as those carried out in blast furnaces and other apparatus for smelting and steel-making) produce extremely serious dust problems if the fine material were not transformed into the hard and mechanically resistant pellets or similar forms.
A key characteristic of mill scale is that it is a largely comprised of small particles “fines” rich in iron oxide. If simply dropped into the furnace these “fines” are often entrained by the high velocity air blast permeating the blast furnace and quickly ejected from the system. A portion of those fines that are not ejected can seriously clog and impede the passage of blast gases upward through the furnace thus reducing its efficiency. These problems have led to the various very expensive and energy-consuming processes now used to re-cycle limited amounts of mill scale. Briquetting, for example, compacts the mill scale plus binders into roughly biscuit-sized agglomerates that are relatively well suited to the blast furnace environment But besides being inefficient and expensive compared to the system and methods disclosed herein, such processing for recovery of the iron in mill scale is typically done only with relatively clean scale. Oily and grease-laden mill scales, which have accumulated in large quantities over many decades throughout the world, are not well-suited to such methods because binders do not work well with such materials.
Due to these technical and cost issues, hundreds of millions of tons of mill scale have accumulated in the US alone. The mere cost of placing mill scale in landfills or “dumps” can currently reach seventeen to thirty-five dollars per ton. Other metallurgical waste fines present similar problems. The disclosed method eliminates disposal costs by providing an economical method for recycling fines that does not use binders or sintering processes, avoids dust dispersal, avoids pollution from vaporized hydrocarbons in oily fines, and can use carbon-containing fines in combination with the metallurgical fines to contribute process energy (BTUs) and components for desirable chemical reactions such as oxide reduction.